The secret life of gamma-Cas, revealed

High-resolution observations made by XRISM have revealed the origin of the curious X-rays coming from naked-eye star gamma-Cas: matter falling onto its companion, a white dwarf star.

Gamma-Cas is classified as a ’Be’ star, merging the ‘B’ associated with hot blue-white massive stars with the ‘e’ from a peculiar hydrogen signature in the light coming from a rotating disc of matter ejected by the fast-spinning star. This matter is forming a disc around a nearby white dwarf star (a compact object with the mass of the Sun but the size of Earth). The matter falls towards the star’s poles along the white dwarf star’s intense magnetic field, and generates X-rays.

XRISM’s high-precision observations finally show that the X-rays closely follows the orbital motion of the white dwarf, and not gamma-Cas itself. This closes the case on a mystery that has puzzled astronomers for more than fifty years. 

Read more

[Image description: Image with text and a bold, red-highlighted title: ‘XRISM solves 50-year X-ray mystery’. A large ball shines in shades of white and blue over a black background. The ball is surrounded by a light-blue and white disc with a fuzzy texture, like that of a dense gas. The disc connects by a bluish ribbon to a smaller disc surrounding a smaller glowing-white ball, located in the lower left of the image. Two light-blue, shiny, arches of gas shoot out from opposite sides of the smaller disc and meet at the top-pole of the smaller ball. From this pole three wiggly, red arrows, shoot upward. They are labelled ‘X-rays’.]